This invention relates to an arbor which can be mechanically expanded to clamp a series of workpieces or other elements when the workpieces are positioned in a face-to-face relationship along the length of the arbor. More specifically, the arbor is characterized by structural features which provide for progressive clamping of a series of workpieces in a sequence beginning at one end of the arbor and ending at an opposite end thereof.
Various types of expandable arbors have been devised for clamping and securing one or more workpieces or other elements having cylindrical bores therethrough. It is known, for example, to utilize a series of expandable collets, or similar structures, which can be expanded through a wedging action of such collets against one another or against adjacent structures having tapered surfaces similar to those on the individual collets. The collets themselves are typically formed with one or more slots that permit a circumferential expansion of the collet as it is wedged in an axial direction against a mating structure. Patents showing representative structures of this type include U.S. Pat. Nos. 2,573,928; 2,734,749; 2,755,093; 3,073,610; 3,009,747; and 3,192,820.
As shown in U.S. Pat. Nos. 2,573,928 and 3,073,610, it is also known to provide for the clamping of a series of stacked workpieces or other elements with an arbor made up of a sufficient number of expanding collets to match the number of workpieces or elements to be clamped. FIG. 6 of the U.S. Pat. No. 2,573,928 illustrates the clamping of a series of separate milling cutters on a series of rings which can be mechanically expanded to grip the bores of the separate milling cutters. The drawings of U.S. Pat. No. 3,073,610 show a similar arrangement for a series of stacked workpieces which are gripped at their central bores through an expansion of rubber rings.
The present invention is primarily concerned with solving a problem of clamping a number of cylindrical workpieces for the purpose of holding a stack of such workpieces in a very rigid and known relationship to cutting or grinding elements functioning to form the stack of workpieces into a number of identical spur or helical gears. The workpieces themselves have a characteristic of being manufactured within a limited tolerance range for dimensions of their central bores and their outside diameters. In attempting to apply known principles of clamping to the requirements of this job, it was soon learned that there are a number of difficulties in achieving complete, rigid clamping of each of a series of workpieces with an arbor having a series of collets for being expanded into engagement with the individual bores of the workpieces. Very slight differences in bore sizes create a special problem of achieving a complete clamping of each and every such workpiece through the use of expanding collets which are mechanically compressed together in an axial direction to achieve radial expansion of the individual collets of the series. It was found, for example, that an undersized workpiece in the middle of the stack will tend to disrupt a progressive expansion of each adjacent collet in the series, and workpieces above or below the position of the undersized part might receive insufficient clamping from their associated collets as a result of this disruption in sequential clamping.
In order to solve this problem, it was decided to attempt to achieve a more certain sequencing of expansion of individual collets in the series, and it was decided to devise means for carrying out initial clamping at an end of the series which is remote from the end to which a clamping force is applied. After clamping is achieved at the one end of the stack of workpieces, each successive workpiece is then clamped in a sequence which progresses from the end of the first clamping to the opposite end of the stack. In this manner, full and complete clamping of each workpiece can be achieved.
In order to accomplish such sequential clamping, the arbor of this invention was designed with a variable force requirement for expanding each collet in a series of such collets, and the variable force requirement is progressively greater toward one end of the series than it is toward an opposite end thereof. One way of providing such a variable force requirement for individual collets is to design the separate collets of a series with variable spring rates. "Spring rate" as used in the descriptions herein is intended to describe the ease with which a metal, or other material, collet can be expanded radially from its normal configuration when it is at rest. Variable spring rate can be provided by varying the thickness of the material from which each collet is manufactured or by varying the number of slots formed in the individual collets. Maximum variation can be achieved by combining variations in thickness and number of slots.
Another way of providing a variable force requirement for expanding a series of collets is to vary the outside diameters of the individual collets so that a greater force will be required to expand a smaller diameter collet out to its gripping position when compared with the force required to expand a larger diameter collet out to a similar gripping position. This type of variation in collet design can be combined with the variations in material thickness and number of slots if desired.
In a specific embodiment of the invention an arbor is provided for clamping and holding a stack of cylindrical workpieces while the workpieces are manufactured into spur or helical gears. The arbor includes a series of expandable collets equal in number to the number of workpieces to be carried by the arbor, and each collet comprises a cylindrical member having a base portion for contacting the hub of the arbor and an expandable portion for contacting the bore of a workpiece to be held by the arbor. The base portion of each collet carries an outer tapered surface, and the expandable portion of each collet has an inner tapered surface for mating with the outer tapered surface of the base portion of a next adjacent collet when a series of such collets are stacked in overlapping relationship on the hub of the arbor. In this way, the collets can be expanded by an axial movement of a first collet into wedging engagement with a next adjacent collet, with the movement being transmitted down the entire series until a last collet of the series is reached.
In order to provide a needed sequence of clamping of the individual collets, it is important that axial movement of the entire series of collets takes place before a collet at a remote end from the end to which the clamping force is applied is radially expanded to effect a clamping of its associated workpiece. This is done by varying the spring rates, the number of slots, or the outside diameters of the individual collets in the series so that the last collet of the series is more easily radially expanded to its full gripping position before each successive collet is expanded to its respective gripping position.
In addition to utilizing a variable force requirement for expanding the series of collets, the invention may optionally utilize a series of rings carried on the arbor in positions between each workpiece placed on the arbor. The rings carry pin members for insertion into openings formed into the workpieces to effectively secure each of the workpieces of the stack to other workpieces of the stack.
These and other features of the invention will become more apparent in the detailed discussion which follows. In that discussion, reference will be made to the accompanying drawings, as briefly described below.